In-situ ATR-FTIR spectroscopic study of electro-oxidation of methanol and adsorbed CO at Pt-Ru alloy

Methanol oxidation reaction (MOR) has been investigated at sputtered Pt-Ru, Ru, and Pt electrodes by using in-situ FTIR spectroscopy with the attenuated total reflection technique (ATR), which can identify species adsorbed on the electrode surface. Linear CO, bridged CO, and COO- were detected as the intermediates in the MOR. The electro-oxidation of preadsorbed CO was also studied to clarify the mechanism of the MOR at these electrodes. Water molecules coadsorbed with CO were clearly detected at Pt-Ru and Ru electrodes at less positive potential region below the onset potential of ca. 400 mV vs RHE for the electro-oxidation of both methanol and preadsorbed CO. The IR-band intensities of both the adsorbed CO and water commenced to decrease simultaneously at ca. 400 mV on Pt-Ru alloy, demonstrating that the adsorbed CO is oxidized by consuming the adsorbed water. The pure Ru electrode exhibited a high activity for the oxidation of preadsorbed CO, but showed a low activity for the MOR due to the slow dehydrogenation adsorption of the methanol. It is clarified that Pt sites on the alloy surface dehydrogenate methanol and form CO dominantly while Ru sites adsorb water molecules preferentially as oxygen-species needed for the CO oxidation, presumably involved as Ru-OH formed by discharging the adsorbed water. These results support the "bifunctional mechanism" at Pt-Ru alloy for the oxidation of methanol and CO.